Dc. Pineda Group

Cardiovascular disease CVD remains the leading cause of mortality for women and men worldwide, causing about 18 million deaths each year according to the World Heart Federation. It is the number one cause of death in the EU, causing over 6 million new cases each year and over 1.8 million related deaths, causing the EU economy about 210 billion euros. Atherosclerosis is the main pathology underlying ischemic CVD and is characterised by a dysregulation and build-up of lipids and immune cells in the vascular wall of major arteries. Monocytes and macrophages are key cells in innate immune responses and in the initiation and development of atherosclerosis as they orchestrate multiple inflammatory and anti-inflammatory processes. In addition, lipids are critical to the mechanisms underlying adaptation to environmental and internal conditions. Lipids can promote changes in chromatin modifications, which alter chromatin accessibility to transcription factors, including nuclear receptors. What’s more, certain lipids can act as ligands for nuclear receptors as is the case for LXR, leading to changes in the expression of genes, such as those involved in lipid metabolism.

The Liver X Receptors LXRa and LXRb (coded for by NR1H3 and NR1H2 respectively) are ligand-activated transcription factors regulating gene expression (positively and negatively) in a ligand-dependent manner, and that actively control macrophage differentiation and specialization and lipid metabolism. LXR activity is crucially involved in cellular cholesterol metabolism in most tissues. Upon binding of ligands (endogenous oxidised cholesterol derivatives such as oxysterols or intermediates of cholesterol biosynthesis , or synthetic agonists like T0901317 and GW3965), LXR positively control the expression of genes involved in the metabolism of lipid metabolic processes. These collectively inhibit uptake and promote cholesterol efflux, thus contributing to prevent cellular lipid overload. LXR ligands also control inflammation in macrophages by antagonizing the induction of inflammation-related genes after activation and potentiating apoptotic cell clearance. These results have led to recognition of LXR as anti-atherogenic and anti- inflammatory factors. However, LXR activation exacerbates inflammatory responses in human monocytes and other cellular and animal models such as a mouse arthritis model. This apparent contradiction illustrates the ambiguous and complex contribution of LXR to inflammatory and immune responses.

Using our novel knock-in mice models, our group was the first to uncover changes in the phosphorylation of the LXRα receptor as a “sensor” of ongoing metabolic/inflammatory perturbations promoting global chromatin and gene expression changes in fatty liver. We also revealed a novel LXRα phosphorylation-dependent “diet-induced transcriptome”, different from the classic LXR ligand-dependent one, thus redefining our view of how these receptors influence diet-induced responses. Additionally, we identified that disrupting macrophage LXRα phosphorylation affects atherosclerosis progression by altering cell proliferation and phagocytosis through gene expression changes. More recently, we identified a novel mode of action of LXR involving regulation of membrane lipid rafts (specifically cholesterol and glycosphingolipids-GSLs) in lymphocytes (CD4+ T) and reported a GSL biosynthesis enzyme as a novel LXR target. Changes in plasma membrane lipid composition in CD4+-T-cells are associated with altered immune synapse formation, T-cell receptor-mediated signalling, reduced T-cell proliferation and modified cytokine production.

We collaborate with clinical and academic experts and use a range of functional analysis of global high-throughput datasets, animal models and human immune cells, applying our expertise in transcriptomic, metabolomic, lipidomic and proteomic analyses. Continuing from our studies exploring lipid metabolism in human immune cells and our work on cardiovascular risk in women with autoimmunity, our next goal is to investigate cardiovascular risk in women from the general population across their lifespan and uncover the underlying mechanisms to understand these changes. We are working in close collaboration with the Andalusian Biobank, hospitals and donor centres from the region and use experimental mouse models to examine and manipulate therapeutically or genetically the pathways identified. We are investigating variations in circulating lipid levels by NMR-based metabolomic analyses and immune cell gene and protein expression profiles. We will determine whether lipid-activated transcription factors such as LXR, and other transcription factors regulating immune responses such as the interferon response factor IRF8 are partially responsible of the observed changes in gene expression using specific knockout models, some of which we have generated (IRF8), or pharmacological manipulation with LXR agonists and antagonists. We will establish whether sex differences exist in the key processes identified.